Take for example McLaren MP4-29 rear wing design. It has a single slim wing pillar. Pillar starts from a circular shaped support at the end of engine cover. Take a look at this picture:
I find it hard (or at least hardly convenient) to route an hydraulic line all over those parts to get to DRS actuator...
I know I'm probably getting off topic here, but I have same doubts over RB design.
Edit: about electrical/battery, I would find far more easier to route an electrical wire than a hydraulic hose.
Anyway, I'm sure I'm wrong